The application generally relates to the heating of oil in a hermetically sealed compressor. More specifically, the application is directed to the heating of oil in a hermetically sealed compressor with a heating element positioned inside the compressor housing (outer shell) and at least partially submerged within the oil of the oil sump of the compressor.
A hermetic compressor can use oil to lubricate the mechanical components of the compressor. The oil used by the compressor collects in an oil sump located at the base (or lower section) of the compressor housing. During operation of the compressor, the oil is pumped or drawn into the moving compressor components from the oil sump.
One application of a hermetically sealed compressor is in a heating, ventilation, air conditioning and refrigeration (HVAC&R) system. The compressor in an HVAC&R system is used to compress the gaseous refrigerant that is used in the HVAC&R system. However, when the compressor is not operating, some of the gaseous refrigerant in the compressor may condense and drain into the oil sump or be absorbed by the oil if the ambient temperature conditions support the migration of refrigerant into the oil. Such condensation/absorption of the refrigerant can cause dilution of the oil, which may limit the ability of the oil to properly lubricate the mechanical components of the compressor.
In some compressors, the oil in the oil sump can be heated in order to prevent migration of liquid refrigerant into the compressor oil or to evaporate any refrigerant condensate that accumulates in the oil. To heat the oil, a heater assembly can be positioned in a heater well that extends through the compressor housing and is located near the oil sump. However, because of compressor design considerations, the heater well is positioned perpendicularly to, and substantially within, the generally cylindrical side of the compressor housing. The side-mount configuration of the heater well can result in the heater well not always being substantially submerged within the oil of the oil sump. In addition, the heater well may not efficiently transfer heat from the heater to the oil and may cause a significant amount of sound and other vibrations to be projected out into the environment during the operation of the compressor. Further, the use of a heater well requires coating the inside of the well and/or the outer surface of the heater with a heat transfer compound that is subject to dissipation over time resulting in a degradation of heating performance. Another recurring issue with the use of a heater well is refrigerant leaks at the heater well and housing interface due to poor weld joints and cracks that can form in the compressor housing.
Other compressors may use heating elements that are mounted on the exterior wall of the compressor housing and do not function within a heater well. The heating elements used on these compressors heat the housing, which then transfers heat to the oil, resulting in low heating efficiency due to losses to the surrounding air, slow heat transfer to the oil and the heating of the entire housing.
Therefore, what is needed is a heater that is positioned below the oil level of the oil sump and that is fully contained within the compressor housing.